The call will take place at 9 a.m. ET, with Ackman and other Pershing Square portfolio managers and analysts taking questions.

Since taking a position earlier this year, Pershing Square has potentially lost more than $1 billion on paper on Valeant, the fund's largest stock holding.

Shares of the Canadian drug company have collapsed since Wednesday after the California-based short-selling firm Citron Research published a report asking whether Valeant was operating an Enron-like fraud.

Valeant's share price has declined by more than 38% since the report came out.

Valeant has categorically denied the allegations in the Citron report. The company hosted an all-hands call on Monday morning to address the allegations.

Ackman first disclosed his position in Valeant on March 17, when the share price was $200 per share. At that share price, the position was worth $3.9 billion.

With his added shares from last week, Ackman's position is worth $2.36 billion at a closing share price of $110.04 from Monday. That would represent a loss of around $1.5 billion.

Valeant's stock has come under pressure in recent months. In late September, Democrats on the House Oversight and Government Reform Committee sent a letter to the committee's chairman, Jason Chaffetz (R-Utah), asking him to subpoena the pharmaceutical company for documents related to price increases of acquired drugs.

At the Bloomberg Most Influential Conference earlier this month, Ackman said drug repricing was a very small part of Valeant's business.

He later added: "Valeant has made a massive contribution to drug development, more so than almost any other company."

In the spring of 2014, Ackman teamed up with Valeant to pursue a hostile takeover of Allergan, the maker of Botox. All of Ackman and Valeant's offers were rejected.

At the time, Ackman didn't own any shares of Valeant. He couldn't own Valeant shares while working with the company on the takeover.

Pershing Square was the best-performing hedge fund last year, returning 40.4%. This year is a different story.

Pershing Square Holdings, the publicly traded vehicle for the fund, was down 11.2% for the year to October 20 before the Valeant collapse. The latest performance data for the fund is expected to come out Wednesday afternoon.

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